Since man first began to build free-standing structures, the problem of reducing heat loss has been a problem. Prior to the advent of inexpensive fossil fuels, only the inherent insulating qualities of the building materials themselves were used to control heat losses.
During the years of inexpensive fossil fuels there was very little concern with improving insulation for either building structures or equipment applications since the cost of insulating was generally much greater than the cost of the additional fuel to compensate for the heat loss.
With the sharply increasing cost of fossil fuels and the less availability of the same, insulation in more modern times has become an increasingly important technology. Ratings of various types of insulation have been standardized according to their insulation value and are referred to as "R-ratings". Products such as rock wood and fiberglass have been used to increase the insulation value for both structures and products where heat loss is a problem.
In more recent years, expanded ceramics have been experimented with as an insulating material. An example of such a product that is now commercially available is expanded perlite with a sodium silicate coating sold under the trade name "Fire-Guard" produced by Applied Ceramic Technology, Inc., of Rochester, Ind. This is a loose granular material which can withstand temperatures up to 2000 degrees Fahrenheit. Use of this material in building structures has been claimed to have an insulation value of R-70 for three inches of material. Laboratory tests, however, have disputed this claim with results showing R-8.1 for the same thickness or a R-value of 2.7 per inch versus the claimed 23.3 per inch. Although some validity for the higher claimed R-value may reside in moisture absorption and evaporation during cyclic periods, ceramic insulation certainly in and of itself does not have a stable high R-value.
Foam plastics such as urethane have an accepted higher R-rating than expanded ceramics (R-2.7 per inch for expanded perlite versus R-7 per inch for expanded urethane). The urethane, however, can only withstand surface temperatures in the neighborhood of 250 degrees Fahrenheit versus 2000 degrees Fahrenheit for the ceramic. Although urethane is used for insulating such things as coolers and drink containers, the same has not been widely accepted for uses such as insulating of water heaters and building structures because of its relatively low surface heat resistance.